We have developed an experimental protocol in which we are able to measure simultaneously from an in situ ileal loop changes in the Starling forces of the intestine under a variety of physiological conditions. The forces measured are capillary hydrostatic pressure, plasma and lymph colloid osmotic pressure, lymph flow, changes in intestinal volume and capillary filtration coefficient. Additional parameters that are measured are intestinal blood flow, arterial and venous pressure, changes in blood pH and hematocrit, A-VO2 extraction and A/G ratios of plasma and lymph proteins. From the above data, interstitial fluid pressure can be calculated, and a pressure-volume curve of the tissue plotted. We propose to measure the forces and flows of capillaries and tissue spaces during perturbation in arterial (autoregulation) or venous pressure (myogenic), drug induced vasodilation or vasoconstriction, hemodilution resulting from infusions of fluids, glucose induced mucosal absorption and cholera toxin induced mucosal secretion. The understanding of the changes in the forces and flows will contribute in establishing a basic working model of the intestine in states of health and disease.